Global warming alarmists are retreating from their longstanding denial of the Pacific Decadal Oscillation’s role in global temperatures. This is a welcome development in terms of scientific truth, but their retreat is due more to strategic chicanery than a newfound commitment to sound science.

As global temperatures rose between the late 1970s and the late 1990s, global warming realists pointed out the cyclical Pacific Decadal Oscillation (PDO) was in a warm mode, providing natural enhancement of whatever human induced global warming was occurring. The Pacific Decadal Oscillation describes water conditions in the tropical Pacific Ocean that drive global climate conditions. Scientists have long observed the PDO alternates between warm and cool modes, switching back and forth every few decades. Alarmists downplayed the PDO at the time, asserting greenhouse gas emissions were responsible for all or virtually all of the 20-year warming during the PDO warm phase. This denial enabled alarmists to project long-term warming at the unusually rapid (relatively speaking) pace of the 20-year warming trend.

Just as climate realists predicted, however, the cyclical PDO eventually switched to its cool mode, sending global warming to a screeching halt. Now that the Earth is well over a decade into a global warming pause, alarmists are suddenly discovering the PDO.

The alarmists’ new mantra is the PDO cool phase is masking rapid warming that will return soon. This is partially correct, in the sense that a warm PDO phase will return at some point and again enhance whatever human induced global warming is occurring. On the other hand, alarmists conveniently fail to mention that the pace of warming during PDO warm phases is, and will continue to be, unsustainable. Long-term global temperature forecasts must average out temperatures between the warm and cool PDO phases.

One of the many reasons alarmist computer models consistently fail to replicate real-world climate conditions is alarmists denied the substantial impact the PDO warm phase had on global temperatures between the late 1970s and late 1990s. Alarmists assumed the pace of warming during warm-phase PDO conditions would continue indefinitely, and then they added other speculative and unjustified warming enhancements, as well. Now that the cool-phase PDO has stifled global warming, alarmists can no longer deny its impact.

That being the case, the long-term pace of global warming – encompassing PDO warm phases and cool phases alike – is, at most, currently 1 degree Celsius per century. Allowing some leeway for future temperatures to warm somehow more rapidly than has been the case for the past century, even a 1.5 degree warming per century undercuts alarmist computer models and Chicken Little future warming predictions.

It is important for alarmists and skeptics alike to understand the PDO alternates between warm and cool phases, such that short-term temperature trends during either phase will indicate more rapid or less rapid warming than will occur in the longer term. The future transition from the current PDO cool phase to a PDO warm phase will likely cause more rapid warming on a short-term scale. That relatively rapid warming will also cease when the PDO switches back to its cool mode.

In the longer term, anthropogenic carbon dioxide emissions will cause some global warming. The best available evidence shows such human induced global warming will be relatively modest and subject to natural swings resulting from ocean cycles, solar variance, and other factors. The Earth continues to warm at a modest long-term pace, still significantly cooler than temperatures that prevailed just a few thousand years ago. At the present pace of warming, we are at least a couple centuries away from anything resembling a global warming problem.